Methods for providing a repair weft thread to remove a faulty weft thread are known, for example from Published European Patent Applications 0,310,804; 0,309,013; and 0,207,470; and U.S. Pat. No. 4,781,221. The disclosure of each of the just mentioned prior patent publications is incorporated herein by reference.
To carry out such known methods a weft thread sensor is provided on the weaving loom opposite the main insertion nozzle for the weft thread. After each insertion of a weft thread, this weft thread sensor monitors whether the weft thread has completely traversed the loom shed. If it has, then the weaving operation continues as usual, i.e. after forming a new shed, a next successive weft thread is inserted. On the other hand, if the inserted weft thread does not arrive at the weft thread sensor, then it is taken as an indication that a weft fault such as a broken thread has occurred and the loom control initiates an automatic process for removing the faulty weft thread. For this purpose the weaving operation is interrupted, the weaving reed is swung back into its starting position, and the weft thread cutting step is blocked or inhibited so that the inserted faulty weft thread that did not traverse the loom shed is not cut off from the weft thread supply. This method, as well as the corresponding specific steps to be taken for carrying it out, is described in more detail in U.S. Pat. No. 4,781,221 or European Patent 0,207,470.
After it has been recognized that the faulty weft thread did not reach the opposite side of the loom and the cutting operation has been interrupted, a new weft thread (known as a repair thread) is inserted onto the faulty weft thread, thereby forming a loop, for example. This loop is now carried by the relay nozzles entirely through the loom shed, i.e. across the weaving width, thereby pulling the faulty thread from the cloth fell or beat-up edge of the cloth. As soon as the inserted faulty weft thread is completely pulled off, i.e. once it has completely traversed the loom shed, it comes into contact with the sensor at the opposite end. This sensor senses and recognizes the weft thread, activates a corresponding suction device to suck the faulty thread and the repair thread from the loom shed, and activates a cutting device that cuts off the repair thread, which is then suctioned out of the loom shed together with the faulty thread. Thereafter the weaving loom returns to normal weaving operation.
If the weft thread that was inserted to repair or remove the thread breakage also gets entangled in the loom shed or suffers another fault and consequently does not arrive at the sensor, then operation of the loom does not resume, but remains stopped.
All of the known technical solutions disclosed in the above mentioned patents operate according to the method described above. A critical point for the known method is that the weft thread cutting operation must be blocked or inhibited before the inserted faulty weft thread is cut off. Otherwise, the broken or faulty weft thread cannot be automatically removed from the cloth fell or beat-up edge by inserting the repair thread as described above.
Practical experience has shown, however, that despite the triggering of a weft fault signal in response to a failure of the thread to arrive at the sensor, the cutting operation cannot always be reliably inhibited. There are many reasons for this. For example, a magnetic switch is used relatively often to interrupt the cutting operation. The response times of these magnetic switches lie typically in the range of several micro-seconds, but are subject to certain fluctuations. These fluctuations can account for up to 20% of the response time of the magnetic switches. Thus, if a faulty weft insertion coincides with an extended response time of a magnetic switch, it is altogether possible that the inserted faulty weft thread is cut despite the intended interruption or blocking of the cutting operation. Further reasons for such fluctuations in the response time include environmental influences such as temperature, humidity, fluctuations in the line voltage, vibrations, and the like. Of course, a simple mechanical error, such as a jam or breakdown or the like, can also cause such fluctuations. Additionally, various electrical fields can transmit error signals to the electrical lines of the loom control; these error signals distort or falsify the control signals and thus prevent the magnetic switch from being triggered. Similar defects can occur not only with magnetic switches, but also with other actuators that are used to interrupt the cutting operation.
Heretofore, the problem of unintended cutting of the faulty weft thread has not been recognized or addressed by those skilled in the art. According to the state of the art, a relatively long repair weft thread is inserted to remove the faulty weft thread. The length of the repair thread is greater than the length of weft thread that is typically inserted for weaving. Thus, if a faulty weft thread has been erroneously cut from the repair thread as described above, then the inserted repair thread is long enough by itself to reach the area of the weft thread sensor without having removed the faulty weft thread from the beat-up edge of the woven cloth. The sensor then recognizes the presence of the repair thread, activates the suctioning-off of this thread after it has been cut, and thereafter allows the continuation of the weaving operation. The disadvantage hereby is that the inserted faulty weft thread remains in the woven cloth and the loom is, so to speak, unaware of the error.
It is determinative for the occurrence of the above described problem that, contrary to the intended operation according to the state of the art, the faulty weft thread is cut from the repair thread that has been made ready, thereby making it impossible to automatically remove the weft fault or breakage in the classic sense. In the classic weft fault repair method, the broken or faulty weft thread must remain connected to the weft repair thread that has been made ready. Otherwise the weft fault will remain in the finished cloth as described above.